1. Field of the Invention
The present invention relates to an improved connector device to connect the end of a composite material rod. In particular, the present invention relates to improvements to a connector to connect the end of the composite material rod so that rods are connected therein in an end-to-end relationship.
2. Prior Art
The use of cylindrical sucker rods is well known in underground wells to actuate a pump located in an underground wellbore of a well. A series of sucker rods connected together in an end-to-end relationship form a string which extends down into the wellbore. The string is connected to a subsurface pump at one end and to a reciprocating mechanism at the well head on the surface at the other end in order to actuate the pump to lift well fluids to the surface.
While at one time steel sucker rods were common, over the last three decades the oil and gas industry has been using fiberglass for sucker rods and, more recently, using composite matrix material, such as fiberglass composite, graphite composite, metal matrix composite, ceramic matrix composite or other composite matrix materials, for sucker rods. Composite matrix material rods are advantageous over metal because they are lighter than metal, withstand corrosive effects better than metal and have greater elasticity than metal, and are advantageous over fiberglass because they are stronger than fiberglass while having the same advantages of fiberglass.
The individual composite material rods are connected together by metal connectors (also sometimes called end fittings) that are generally elongated members having an axial receptacle. The connector will typically have an opposite threaded end so that a pair of connectors may be secured together. The composite material rod may be connected to the connector through use of an adhesive which will bond to the rod. Once the adhesive adheres to the rod and becomes a solid, it is referred to as a wedge and a plurality of wedges in the connector is referred to as a wedge system.
Various designs have been suggested to produce a good bond and attachment between the rod and the adhesive to create a wedge system that is captured within the annuluses of the connector to create a sucker rod. Two operational limitations of composite sucker rods, however, still leave much room for improvement: (1) the ability of the sucker rod to endure the hostile operating and loading conditions in which they operate and (2) the difficulty of retrieving a broken composite matrix material sucker rod from the wellbore.
Examples of prior connector designs are disclosed in Anderson et al. (U.S. Pat. No. 4,653,953), Iwasaki et al. (U.S. Pat. No. 4,822,201) and Rutledge, Jr. et al (U.S. Pat. No. 4,919,560). These designs teach a connector that has a series of wedge or partial cone-shaped annulus recesses extending from the receptacle into the body of the connector that are used to form the wedge system within the connector. Some of these prior designs recognized that radial stresses are not constant across the wedge system and therefore varied the angle of inclination from one wedge to the next.
In order to make the attachment of the rod to the metal connector, an initially flowable adhesive is placed in the receptacle of the connector. A rod end is then inserted into the receptacle. The insertion of the rod forces the flowable adhesive to fill the void spaces in the wedge-shaped or partial cone-shaped recesses. The adhesive will cure becoming a solid and will adhere to the rod. The solid adhesive is bonded to the rod and not to the inside of the metal connector. The solid adhesive bonded to the rod forms a series of wedges, having the shape of the recesses within the connector to create the wedge system that captures the rod within the receptacle of the connector.
When the assembled rod is pulled by applying tension to its threaded ends, the solid adhesive wedges, which are bonded to the rod only, are forced against the annuluses area of the recesses inside the metal connector. Slippage, which occurs between the rod body and the connector, causes the larger end of the adhesive wedge to separate from the annulus surfaces of the metal connector leaving a slight gap.
A radial compressive force is imparted to the rod itself as the metal connector and the adhesive wedge press against each other to resist any further slippage. This force of compression is applied across the entire interval where the adhesive wedge and the metal surface are in contact. No compression force is applied in the segment adjacent to the gap.
The abrupt change at the end of the gap from no compression force to full, heavy compression force results in a concentration of shear stress at that point, leading to the possibility of failure in the sucker rod.
Accordingly, newer designs were developed to address these failures including Watkins (U.S. Pat. No. 5,233,946) and Rutledge (U.S. Pat. No. 6,193,431). Watkins teaches a connector with a plurality of annuluses where each annulus has an arcuate transition surface at each end of the annulus such that one end of the annulus is tapered to a tangent with the wall of the cylindrical receptacle where the concentration of shear stress is the highest and the other end of the annulus asymptotically approaches the wall of the cylindrical receptacle. Each of the tapered annuluses differs in length and the plurality of annuluses is arranged so that the annuluses decrease in length from the opening of the receptacle. Rutledge teaches a connector with asymptotic transition surfaces between multiple wedges and at the closed end of the connector. These designs are similar to the earlier designs, except for the transition curves at the ends of each annulus that forms the wedge. Both of these designs attempt to reduce the shear stress at the rod surface by eliminating the abrupt angle change at the ends of the wedges that are typical of earlier connector designs. While these designs represented an improvement over prior designs, considerable room for improvement exists.
Also, neither of these designs addresses the further need to retrieve a broken composite material sucker rod from the wellbore with a retrieval tool or, as more commonly referred to in the industry, a “fishing” tool.
Present connector designs have no recess to allow the composite matrix material rod connectors to be grasped by a retrieval tool. In the event that a rod breaks, the well tubing (pipe) inside of which the rods are installed must be pulled out of the well to retrieve the broken rod, or a special retrieval tool must be used to grasp the connector to retrieve the broken rod. These special tools are very expensive and not widely available. Some types of these tools are fragile and often suffer breakage after only one use. Two of these special retrieval tools, for example, are described in Pruitt (U.S. Pat. No. 5,149,163) and Mullane, Jr. (U.S. Pat. No. 6,425,615). Pruitt teaches retrieving composite sucker rods by grasping the wrench flats of the connector. This retrieval tool both grasps and releases the connector with a ⅛ turn of the tool, which is not ideal for retrieval of a broken rod. Mullane, Jr. teaches retrieving the connector by lowering a retrieval tool over the outside of the connector and biting into the outside surface of connector.
Retrieval tool recesses are used in other applications, where various downhole devices are set and/or retrieved from inside tubing and/or the wellbore. The retrieval tool would be lowered into the well from a hoisting device located at the surface. The top of the downhole device that is to be retrieved must be configured such that the retrieval tool will be securely latched onto the downhole device once the two devices are engaged. The upper end of downhole devices that are intended for recovery by this method are typically equipped with a reduced diameter extension or neck with a retrieval tool recess formed near the upper end of the extension. The fingers of the retrieval tool latch into the recess on the reduced diameter extension to establish a secure connection between the retrieval tool and the downhole device. The downhole device can then be pulled from the wellbore by the surface hoisting device. These designs are taught by Williams (U.S. Pat. No. 2,263,910), Brown (U.S. Pat. No. 3,419,075), Plunk (U.S. Pat. No. 3,454,294), Billingsly (U.S. Pat. No. 6,935,427), McCannon (U.S. Pat. No. 7,040,401) and Clemens (U.S. Patent Application No. 2009/0294118). The reduced diameter retrieval extensions described in the above designs have two features that make them unsuitable for retrieving broken fiberglass sucker rods: (1) the geometry of fiberglass sucker rod connectors cannot accommodate a reduced diameter retrieval extension neck as the broken composite matrix material rod occupies the space at the top of the connector that is used for the retrieval extension in other types of applications; as illustrated in FIG. 12 and (2) the open end of the small diameter retrieval tools used in present designs for other applications are too small to capture the splintered body of the broken composite matrix material rod because when a composite matrix material rod fractures, it often creates splintered segments that expand beyond the original diameter of the rod and the reduced diameter retrieval tool cannot capture the expanded rod section.
One fiberglass sucker rod connector by Parsons, Jr. et al. (U.S. Pat. No. 4,433,933) teaches an exterior annular shoulder formed near the open end of the connector by gradually tapering the outer surface inwardly at an angle of 5 degrees for the purpose of allowing the jaws of a retrieval tool to cooperate with the shoulder to retrieve a broken fiber reinforced sucker rod from the wellbore. This design is only effective if the failure of the sucker rod is in the fiberglass rod body above this shoulder. When this fracture occurs, then the shoulder on the exterior of the connector can be engaged by a retrieval tool and the remaining rod string can be removed from the wellbore. If the fiberglass rod connector and coupling connection fails in the wrench flat, threaded pin, or coupling, there is no shoulder that can be grasped by the retrieval tool as shown in FIG. 11. The shoulder that provides a gripping edge is now upside down and will not cooperate with the fingers of the retrieval tool to grasp the connector.
Accordingly, there exists a need to design a rod connector with a plurality of annuluses that will cooperate with a wedge system to spread out the force of compression uniformly along each wedge and eliminate the concentration of radial stress in each wedge.
Also, there is a need to design a rod connector that incorporates a full diameter recess on the exterior of the rod end of the connector to accommodate recovery of broken rods with a retrieval tool.
It is, therefore, a principal object and purpose of the present invention to provide a connector for a composite material rod that will spread out or distribute the force of compression uniformly along each wedge of the wedge system within the receptacle of the connector to eliminate the concentration of radial stress in the wedge.
It is a further object and purpose of the present invention to provide a connector for a composite material rod having wedges with segments with optimum ranges of the ratio of radius length to total wedge length for the connector.
It is also a principal object and purpose of the present invention to provide a connector with a full diameter recess on the exterior of the rod end of the connector to accommodate recovery of broken rods with a retrieval tool.